In production method for a semiconductor device, an adhesive, a die attachment film, or the like which contains liquid epoxy as a main component is used for joining a semiconductor chip to a substrate or the like. The properties of not generating stress to the extent possible in a joined semiconductor chip are required for the adhesive. The stress generated in a semiconductor chip may cause conduction failure in the semiconductor device, due to, for example, detachment between the substrate and the semiconductor chip, or between semiconductor chips facing each other.
Examples of major factors in generating stress in a semiconductor chip include the difference in temperature dependence of shrinkage ratio (linear expansion coefficient) between the semiconductor chip and the cured adhesive material in a step of cooling the adhesive from the heat-curing temperature. In a conventional method, the adhesive is densely filled with an inorganic filler so as to reduce the linear expansion coefficient of the cured adhesive material. Although the cured adhesive material densely filled with an inorganic filler has a reduced linear expansion coefficient, it also has an increased elastic modulus, causing difficulty in sufficiently suppressing the detachment of a semiconductor chip.
In order to deal with the problem, an attempt to use polyimide particles as a filler was made to suppress the increase of the elastic modulus of the cured adhesive material while reducing the linear expansion coefficient. For example, Patent Literature 1 discloses a circuit connecting material having excellent connection reliability and connection appearance, which contains an adhesive composition, conductive particles, and a plurality of insulating particles including one or both of polyamic acid particles and polyimide particles.
In recent years, further downsizing and higher integration have been required for semiconductor devices. The downsizing and thinning of semiconductor chips are thus increasingly ongoing. The polyimide particles having an oversized particle diameter cause problems such that the polyimide particles form foreign substances in an adhesive, that the polyimide particles are pinched during joining of the semiconductor chips, and that the adhesive is not thinned. A method for producing polyimide particles having a smaller particle diameter is therefore required.
Patent Literature 2 discloses, as a method for producing polyimide particles having a small particle diameter, a method for synthesizing polyimide from tetracarboxylic anhydride and diamine compound. Patent Literature 2 discloses a method for producing polyimide particles including: a first step (a) of preparing each of a first solution containing a tetracarboxylic anhydride and a second solution containing a diamine compound; a second step (b) of mixing the first solution and the second solution so as to obtain polyamide acid particles precipitated out of the mixed solution; and a third step (c) of producing polyimide particles through imidization of the obtained polyamide acid particles.
The use of polyimide particles as a substitute for an inorganic filler causes new problems such that the polyimide particles are decomposed under high temperature during production of a semiconductor device and that the voids are generated in an adhesive due to gas generation from the polyimide particles. High heat resistance is, therefore, also required for the polyimide particles. However, polyimide particles having a sufficiently small particle diameter and high heat resistance have not been obtained by any conventional method.